Ultraviolet Death May Follow Asteroid Devastation

Source: OSU News, Oregon State University

Scientists from Oregon State University and the British Antarctic Survey reported in March 2000 that if a huge asteroid were to hit Earth, the catastrophic destruction it would cause, and even the “impact winter” that would follow, might only be a prelude to a different but very deadly phase that would start later on. They're calling it “ultraviolet spring.”

Andrew Blaustein, a professor of zoology at Oregon State University, and his colleague Charles Cockell, a researcher with the British Antarctic Survey, examined secondary ecological repercussions of a major asteroid impact of a magnitude similar to the one that occurred around the Cretaceous-Tertiary, or K-T, boundary. This asteroid is believed to have hit off the Yucatán Peninsula with a force of almost one trillion megatons. At the time, there was a massive extinction of many animals, including the dinosaurs.

The immediate result of an asteroid impact would be devastating destruction and an impact winter, with widespread death of plants and the large terrestrial animals—including humans—that most directly depend on those plants for food. Such an impact would also load the atmosphere with nitric oxide, causing massive amounts of acid rain. As they became acidified, the lakes and rivers would have reduced amounts of dissolved organic carbons, thereby allowing for much greater penetration of ultraviolet light.

At first, the ultraviolet rays would be blocked by the global dust cloud that would blot out the sunlight and choke the planet in icy winter-like conditions for months. During the extended winter, animals across the biological spectrum would starve and become weaker, and many would die. The researchers calculated that the dust cloud would shield Earth from ultraviolet light for an extended period of about 390 days before the dust settled and the ultraviolet radiation returned to its level before the impact. After that, the ozone depletion would cause ultraviolet levels to at least double, about 600 days after impact.

According to their study, these factors would lead to ultraviolet-related DNA damage about 1,000 times higher than normal and general ultraviolet damage to plants about 500 times higher than normal. Ultraviolet radiation can cause mutations, cancer, and cataracts. It can kill plants or slow their growth, suppressing photosynthesis, which forms the base of the world's food chain.

The researchers said that smaller asteroid impacts, which have happened far more frequently in Earth's history, theoretically might cause similar or even worse problems with ultraviolet exposure. The ozone depletion would be less, but there would also be less of a protective dust cloud.

During the K-T event, the scientists said, many of the animals may actually have been spared most of the ultraviolet spring they envision. That impact, oddly enough, hit a portion of Earth's crust that was rich in anhydride rocks. This produced a 12-year sulfide haze that blocked much of the ultraviolet radiation. But it was a lucky shot because that type of rock covers less than one percent of Earth's surface.

Part of what the scientists are trying to stress is that with an asteroid collision, there will be many synergistic effects on the environment that go far beyond the initial impact. They warn that when the next “big one” comes, the collision will be devastating and the impact winter deadly, but it will be the ultraviolet spring that may finish off the survivors.